A customer showed me this the other day. At the crown of a hat (or in the shoulder of a sweater) while you are weaving in ends, leave an extra-long bit of yarn, but shorten it by chain crocheting it. That way you’ll have easily accessible yarn for mending that has the same amount of washing and wearing as the finished item.
I thought it was a really smart approach, and I hope I will remember to do it in the future.